I installed wxWidgets using Darwinports (wxWidgets @2.6.3_0+darwin_8 (active)).
The DarwinPorts website for wxWidgets is quite unhelpful (http://darwinports.opendarwin.org/ports/?by=name&substr=wxwidgets), but it could also be, as you say, a bison problem. Try upgrading both bison and flex.
Dave.